The world airline industry is expected to take a massive $10 billion hit this week because of Tuesday’s vicious sneak attacks on the World Trade Center and the Pentagon.

The International Air Transport Association estimates the 266 airlines it represents are losing money rapidly as they maintain grounded planes and pay workers and other expenses.

Some 40 percent of a carrier’s costs continue even when its planes aren’t flying, industry consultants said.

Standard & Poor’s is considering cutting the long-term credit ratings of all U.S. airlines, as well as British Airways and Air Canada, Bloomberg reported.

The airlines, which are already having their worst year in a decade, would find the cost of borrowing money raised even higher.

Air travel is expected to be much reduced in coming months, as frightened travelers avoid flying.

Three weeks ago, IATA predicted losses for the global airline industry this year at $6 billion. “We’re now looking at $10 billion,” said spokeswoman Martine Malka, “although that’s a ballpark figure. It looks like a huge decline.”

Malka said the U.S. air travel market is worth around $1 billion a day in revenue.

But the major losses will come from a slowdown in demand plus the added expense of implementing new security measures.

Midway Airways has already succumbed, announcing it was closing just hours after the first attack. The company fired its staff of 1,700, saying it doesn’t have the resources to reorganize if demand plunges farther. AMR, the largest airline company, UAL Corp.’s United Airlines and other U.S. carriers now stand to lose a combined $4.4 billion this year and as much as $400 million next year, UBS Warburg analyst Sam Buttrick said in a report.

Buttrick had expected the carriers to have a profit of $700 million next year. Higher security and fuel costs will contribute to the widening loss, Buttrick said, adding that there will be an “unprecedented” effect on revenue and earnings.

The Federal Aviation Administration on Tuesday grounded the nation’s 36,000 to 40,000 daily flights after hijackers seized jetliners from American and United for murderous suicide attacks.

The U.S. government allowed limited travel to resume yesterday, with new restrictions on luggage and check-ins at airports. Some 145 airports were cleared to reopen.

It could be days before the U.S. air system is back to capacity, carrying up to 2 million passengers a day.

The only big carriers expected to make a profit this year are Continental Airlines and Southwest Airlines, said Thomson Financial/First Call.

European airlines will also be hit by a decline in transatlantic traffic.

Meanwhile, Boeing Co., the largest airplane maker, said it won orders for 10 of its 737 jetliners worth approximately $550 million. The company declined to say who placed the order.